1. Field of the Invention
The present invention generally relates generally to the field of fluid control elements. More particularly, the present invention relates to the field of low-energy electrical water flow control devices that conserve energy and reduce the waste of water.
2. Description of the Related Art
Automatic faucets have become popular for a variety of reasons. They save water, because water can be run only when needed. For example, with a conventional sink faucet, when a user washes their hands the user tends to turn on the water and let it run continuously, rather than turning the water on to wet their hands, turning it off to lather, then turning it back on to rinse. In public bathrooms the ability to shut off the water when the user has departed can both save water and help prevent vandalism.
One early version of an automatic faucet was simply a spring-controlled faucet, which returned to the “off” position either immediately, or shortly after, the handle was released. The former were unsatisfactory because a user could only wash one hand at a time, while the later proved to be mechanically unreliable.
A better solution were hands-free faucets. These faucets employed a proximity detector and an electric power source to activate water flow without the need for a handle. In addition to helping to conserve water and prevent vandalism, hands-free faucets also had additional advantages, some of which began to make them popular in homes, as well as public bathrooms. For example, there is no need to touch the faucet to activate it; with a conventional faucet, a user with dirty hands may need to wash the faucet after washing their hands. In public facilities non-contact operation is also more sanitary. Hands-free faucets also provide superior accessibility for the disabled, or for the elderly, or those who need assisted care.
Typically, these faucets use active infra-red (“IR”) detectors in the form of photodiode pairs to detect the user's hands (or other objects positioned in the sink for washing). Pulses of IR light are emitted by one diode with the other being used to detect reflections of the emitted light off an object in front of the faucet. Different designs use different locations on the spout for the photodiodes, including placing them at the head of the spout, farther down the spout near its base, or even at positions entirely separate from the spout.
For both safety and cost reasons it is preferable to use battery power to operate hands-free faucets, so power consumption is an important design consideration. Because the detection devices require very little power to operate, the most significant power consumption comes from the mechanical operation of the valve to physically regulate the flow of water.
Naturally, the mechanical operation of the valve must be suitable for electronic control, since it must be responsive to the output of the IR detectors. Proportional control valves provide a useful means for electronic control of the valve mechanism. An example of a proportional control valve mechanism (used to control fluid flow in a water heater) is disclosed in U.S. Pat. No. 5,020,771 to Nakatsukasa, which is hereby incorporated herein in its entirety.
FIG. 1 is a diagram of a proportional control valve mechanism, indicated generally at 100. The proportional control valve mechanism 100 includes a main valve 120, which provides the main mechanical control of the flow, and a pilot valve 140, which is used to regulate the main valve 120. Fluid enters the proportional control valve mechanism 100 at 101, and travels through a main passageway 103, which leads to a first chamber 110.
The chamber is defined in part by the main valve 120, and by a first side of a diaphragm 112 that is approximately the same size as the main valve 120 opposite the main valve 120. The diaphragm 112 is connected to the main valve 120 by a shaft 122. Because the main valve 120 and the diaphragm 112 are approximately the same size, pressure in the chamber 110 results in an equal and opposite force on the shaft 122.
A portion of the main flow is diverted to the pilot valve 140 through a first bypass passageway 105. The pilot valve 140 is connected to a solenoid 142, which operates the pilot valve 140 in response to an electronic signal, such as a dithered pulse-width modulated (“PWM”) signal.
When the pilot valve 140 is open, the diverted flow passes through a second bypass passageway 107 into a second chamber 109. The second chamber 109 is defined in part by a second side of the diaphragm 112, opposite the first chamber 110, and contains an orifice 111 that permits the diverted fluid to return to the main flow downstream of the main valve 120. Consequently, when the pilot valve 140 is opened pressure on the second side of the diaphragm generates force that disturbs the balance of forces on the shaft 122 from the pressure within the first chamber 110. The magnitude of the pressure in the second chamber 109 is a function of the size of the orifice 111 and the size of the aperture created by opening the pilot valve 140. Thus, the net force on the shaft 122, and hence how far it will deform the diaphragm 112 and open the main valve 140, can be controlled by controlling the flow through the pilot valve 140.
Because the pilot valve can be substantially smaller than the main valve, it can experience less force from the fluid pressure, and require less energy to actuate. Furthermore, even a relatively small displacement in the pilot valve 140 can produce enough pressure to cause a substantial displacement in the main valve 120. Consequently, the actuation of the pilot valve 140 requires substantially less power than it would require to actuate the main valve 120.
Nevertheless, the proportional control valve mechanism 100 requires continuous power in order to maintain flow. When power to the solenoid 142 is cut, the diverted flow forces the pilot valve 140 closed. Since the second chamber 109 has an orifice, fluid will exit through it until there is no internal pressure. Consequently, the diaphragm 112 returns to its undeformed position, and the main valve is closed. In applications in which power is supplied by batteries, the continuous draw of power to maintain flow leads to the need to replace batteries relatively frequently.
Thus, what is needed is a means to regulate the flow of water in a hands-free faucet which draws very little power, to reduce the frequency with which batteries must be replaced. In particular, there is a need for a means to regulate the flow of water in a hands-free faucet which does not draw power during steady-state operation—that is, it only draws power to change the flow rate. The present invention is directed towards meeting these needs, among others.